[PATCH] libstdc++: Use _GLIBCXX_USE_BUILTIN_TRAIT for is_same

[Ken Matsui]

Since is_same has a fallback native implementation, and
_GLIBCXX_HAVE_BUILTIN_IS_SAME does not support toggling which
implementation to use, we remove the _GLIBCXX_HAVE_BUILTIN_IS_SAME
definition and use _GLIBCXX_USE_BUILTIN_TRAIT instead.

libstdc++-v3/ChangeLog:

        * include/bits/c++config (_GLIBCXX_HAVE_BUILTIN_IS_SAME):
        Removed.
        * include/std/type_traits (is_same): Use
        _GLIBCXX_USE_BUILTIN_TRAIT instead of
        _GLIBCXX_HAVE_BUILTIN_IS_SAME.
        (is_same_v): Likewise.

Signed-off-by: Ken Matsui <kmat...@gcc.gnu.org>
---
 libstdc++-v3/include/bits/c++config  | 4 ----
 libstdc++-v3/include/std/type_traits | 9 +++++----
 2 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/libstdc++-v3/include/bits/c++config 
b/libstdc++-v3/include/bits/c++config
index ad07ce92d5f..b57e3f338e9 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -845,10 +845,6 @@ namespace __gnu_cxx
 # define _GLIBCXX_HAVE_BUILTIN_IS_AGGREGATE 1
 #endif
 
-#if _GLIBCXX_HAS_BUILTIN(__is_same)
-#  define _GLIBCXX_HAVE_BUILTIN_IS_SAME 1
-#endif
-
 #if _GLIBCXX_HAS_BUILTIN(__builtin_launder)
 # define _GLIBCXX_HAVE_BUILTIN_LAUNDER 1
 #endif
diff --git a/libstdc++-v3/include/std/type_traits 
b/libstdc++-v3/include/std/type_traits
index a9bb2806ca9..21402fd8c13 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -1470,16 +1470,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // Type relations.
 
   /// is_same
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_same)
   template<typename _Tp, typename _Up>
     struct is_same
-#ifdef _GLIBCXX_HAVE_BUILTIN_IS_SAME
     : public __bool_constant<__is_same(_Tp, _Up)>
+    { };
 #else
+  template<typename _Tp, typename _Up>
+    struct is_same
     : public false_type
-#endif
     { };
 
-#ifndef _GLIBCXX_HAVE_BUILTIN_IS_SAME
   template<typename _Tp>
     struct is_same<_Tp, _Tp>
     : public true_type
@@ -3496,7 +3497,7 @@ template <typename _Tp>
 template <typename _Tp, unsigned _Idx>
   inline constexpr size_t extent_v<_Tp[], _Idx> = extent_v<_Tp, _Idx - 1>;
 
-#ifdef _GLIBCXX_HAVE_BUILTIN_IS_SAME
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_same)
 template <typename _Tp, typename _Up>
   inline constexpr bool is_same_v = __is_same(_Tp, _Up);
 #else
-- 
2.43.0